Vitamin D fortification of foods - sensory, acceptability, cost, and public acceptance considerations.

In terms of vitamin D food fortification, there are a number of important considerations in relation to selection of the food vehicle and fortificant. While there has been much research focus on the ability of fortified foods to improve vitamin D status, other considerations, such as sensory properties and acceptability, cost, and public attitudes around vitamin D-fortified foods, have received less attention. Thus, the present narrative review aimed to summarize the existing knowledge around these important considerations. In summary, its findings suggest that: i) vitamin D addition to various food vehicles, at levels consistent with the supply of part or all the recommended intake, does not alter their sensory characteristics or overall acceptability; ii) overall, vitamin D fortification of foods is relatively cost-effective, despite the fact that some attitudinal studies highlighted participant concerns about the potential cost/expense of vitamin D-fortified foods; iii) evidence from various attitudinal studies suggest a high level of acceptance and/or purchase intention (i.e., extent to which customers are willing and inclined to buy) of vitamin D-fortified food products by the general public; and iv) there have been repeated calls for vitamin D public health educational/information campaigns to help educate consumers about the health risks associated with vitamin D deficiency and nutritional benefits associated with consumption of vitamin D-fortified foods. Such campaigns could positively mediate attitudes and acceptance of vitamin D-fortified foods amongst the public, and could also help address misconceptions and allay fears around vitamin D for concerned individuals. Lastly, the findings of the present review also highlight the existence of between-country differences, even within Europe, in relation to attitudes and purchase intention of vitamin D-fortified foods and the perceived appropriateness of certain food vehicles for vitamin D fortification, as well as the best mix of communication channels for a vitamin D public health educational/information campaign.

Assessment, treatment and prevention of vitamin D deficiency.

Vitamin D deficiency is prevalent among various groups in the UK, and can result from insufficient sunlight exposure and dietary intake. There is a population-wide recommendation of 10 micrograms (400 international units) of vitamin D per day, with a daily supplement advised. However, supplement use is often suboptimal, compounding the risk of deficiency. Long-term vitamin D deficiency can cause rickets in children and osteomalacia or osteoporosis in adults. Therefore, it is important that nurses recognise which groups are at increased risk of vitamin D deficiency and understand how to assess people's vitamin D status. Nurses also need to be able to support the prevention and treatment of low vitamin D levels, which typically involves supplementation and lifestyle changes.

Longitudinal Assessment of Serum 25-Hydroxyvitamin D Levels during Pregnancy and Postpartum-Are the Current Recommendations for Supplementation Sufficient?

(1) Background: Pregnant women are at risk of vitamin D deficiency. Data on pregnancy outcomes in women with vitamin D deficiency during pregnancy are controversial, and prospective longitudinal data on vitamin D deficiency with consistent definitions in pregnant women are scarce. (2) Methods: The aim of this prospective longitudinal cohort study was to investigate 25-hydroxyvitamin D levels over the course of pregnancy and postpartum in singleton and twin pregnancies with regard to dietary and supplemental vitamin D intake and environmental factors influencing vitamin D levels, evaluated by a standardized food frequency questionnaire. (3) Results: We included 198 healthy singleton and 51 twin pregnancies for analysis. A total of 967 study visits were performed over a 3-year period. Overall, 59.5% of pregnant women were classified as vitamin D deficient in the first trimester, 54.8% in the second trimester, 58.5% in the third trimester, 66.9% at birth, and 60% 12 weeks postpartum, even though 66.4% of the study population reported daily pregnancy vitamin intake containing vitamin D. Dietary vitamin D intake did not affect vitamin D levels significantly. (4) Conclusions: The majority of pregnant women evaluated in this study were vitamin D deficient, despite administration of pregnancy vitamins containing vitamin D. Individualized vitamin D assessment during pregnancy should be considered to ensure adequate supplementation and prevention of hypovitaminosis D.

An Assessment of Risk Factors for Insufficient Levels of Vitamin D during Early Infancy.

Recent evidence suggests that breastfeeding may increase the risk of vitamin D deficiency in offspring. However, it is unclear whether increased risk results from breastfeeding alone, or whether it is associated together with other risk factors. This study surveyed 208 infant-mother dyads recruited by stratified random sampling in different districts of Hong Kong. Mothers were asked to complete a questionnaire on their demographics, history of risk behavior, and feeding practices. Peripheral blood samples were collected from infants to determine their vitamin D status. Among all infant participants, 70 were vitamin D insufficient or deficient. Being breastfed, being a girl, having a multiparous mother, and the use of sun cream were found to be the strongest risk factors for vitamin D insufficiency during infancy (all p < 0.05), after mutual adjustment. The cumulative risk model displayed a dose-response pattern between the number of risk factors and the risk of vitamin D insufficiency during this period. Our findings indicate the risk profile of infants with insufficient vitamin D. Guidelines and recommendations on healthy diet and lifestyle should be provided to mothers during the early stage of pregnancy to increase the likelihood of adequate levels of vitamin D in their offspring.

Assessment of knowledge, attitudes and practice towards Vitamin D among university students in Pakistan.

BACKGROUND: Pakistan has one of the highest reported incidence of vitamin D deficiency in studies conducted worldwide. However, there has been very limited exploration of vitamin D related knowledge, attitudes and practices among healthy youth in Pakistan. METHODS: A cross-sectional survey was conducted among youth (aged > 16 years) from two engineering universities in Pakistan. Participants were asked questions on their concern about vitamin D levels, testing, and supplementation practices. Knowledge was examined using questions about food sources, health benefits and factors affecting vitamin D production within the human body. Of the 900 eligible students invited to participate, 505 (56%) completed the questionnaire and were included in the analysis. RESULTS: Only 9% participants were able to identify the correct food sources of vitamin D, 33% were aware of the bone health benefits (bone health and calcium absorption) of vitamin D and 36% identified sunlight exposure as a factor influencing vitamin D production. Knowledge about food sources and health benefits of vitamin D was not associated with gender and individuals concern about their levels. Those tested and taking supplements were more likely to identify bone related health benefits and factors affecting vitamin D production. Forty percent male and 52% female students expressed concern that their vitamin D levels were too low. However, 72% participants reported that they had never been tested for vitamin D levels. Use of supplements was significantly higher among female students (F = 52% vs M = 37%; P = 0.003). Those who had been tested for vitamin D deficiency were more likely to take supplements. CONCLUSION: Despite being identified as a high-risk population, knowledge about vitamin D was limited among university students. Interventions are needed to increase awareness about the importance of vitamin D for health, including the need for exposure to sunlight and adequate dietary intake of vitamin D. Our study provides much needed baseline evidence for making health-policy recommendations for this vulnerable population group.

The economic case for prevention of population vitamin D deficiency: a modelling study using data from England and Wales.

BACKGROUND: Vitamin D deficiency (VDD) affects the health and wellbeing of millions worldwide. In high latitude countries such as the United Kingdom (UK), severe complications disproportionally affect ethnic minority groups. OBJECTIVE: To develop a decision-analytic model to estimate the cost effectiveness of population strategies to prevent VDD. METHODS: An individual-level simulation model was used to compare: (I) wheat flour fortification; (II) supplementation of at-risk groups; and (III) combined flour fortification and supplementation; with (IV) a 'no additional intervention' scenario, reflecting the current Vitamin D policy in the UK. We simulated the whole population over 90 years. Data from national nutrition surveys were used to estimate the risk of deficiency under the alternative scenarios. Costs incurred by the health care sector, the government, local authorities, and the general public were considered. Results were expressed as total cost and effect of each strategy, and as the cost per 'prevented case of VDD' and the 'cost per Quality Adjusted Life Year (QALY)'. RESULTS: Wheat flour fortification was cost saving as its costs were more than offset by the cost savings from preventing VDD. The combination of supplementation and fortification was cost effective (£9.5 per QALY gained). The model estimated that wheat flour fortification alone would result in 25% fewer cases of VDD, while the combined strategy would reduce the number of cases by a further 8%. CONCLUSION: There is a strong economic case for fortifying wheat flour with Vitamin D, alone or in combination with targeted vitamin D3 supplementation.

Getting underneath the skin: A community engagement event for optimal vitamin D status in an 'easily overlooked' group.

BACKGROUND: Patient and public involvement and engagement (PPIE) is recognized as important for improved quality in health service provision and research. Vitamin D is one area where PPIE has potential to benefit public health initiatives, particularly for women and children with increased skin pigmentation (ie at high risk of deficiency) who are easily overlooked. OBJECTIVE: We report findings from a community PPIE event that explored the knowledge, barriers and promoters for optimal vitamin D status amongst an exemplar high-risk and easily overlooked population group. METHODS: Two researchers and one PPIE lead facilitated a single group discussion with twenty members of the Somali community from across west London. All attendees were women of reproductive age, or knew a mother and child that could benefit from a targeted initiative. The discussion was recorded, transcribed verbatim, organized and coded using NVivo 12 Pro to identify emergent themes underpinned by the Health Behaviour Model. RESULTS: Attendees thought community safety and competing demands of technology and education impacted on sun exposure and lifestyle activity. Language barriers impacted on access to health care. Attendees also felt the mother figure was 'the most important' influencer of both child and wider community health. DISCUSSION: Although further discourse is needed, this event emphasizes that it is important that the public voice is heard in informing, designing and evaluating appropriate public health interventions amongst specific ethnic groups. Insights from this Somali population have suggested benefit from using verbal health messages that are specifically targeted at mothers, compared with the general population.

Vitamin D supplementation and vitamin D status in children of immigrant background in Norway.

OBJECTIVE: Sufficient vitamin D status during infancy is important for child health and development. Several initiatives for improving vitamin D status among immigrant children have been implemented in Norway. The present study aimed to evaluate the vitamin D status and its determinants in children of immigrant background in Oslo. DESIGN: Cross-sectional study. SETTING: Child health clinics in Oslo. SUBJECTS: Healthy children with immigrant background (n 102) aged 9-16 months were recruited at the routine one-year check-up from two child health clinics with high proportions of immigrant clients. Blood samples were collected using the dried blood spot technique and analysed for serum 25-hydroxyvitamin D (s-25(OH)D) concentration using LC-MS/MS. RESULTS: Mean s-25(OH)D was 52·3 (sd 16·7) nmol/l, with only three children below 25 nmol/l and none below 12·5 nmol/l. There was no significant gender, ethnic or seasonal variation in s-25(OH)D. However, compared with breast-fed children, s-25(OH)D concentration was significantly higher among children who were about 1 year of age and not breast-fed. About 38 % of the children were anaemic, but there was no significant correlation between s-25(OH)D and Hb (Pearson correlation, r=0·1, P=0·33). CONCLUSIONS: Few children in the study had vitamin D deficiency, but about 47 % of the children in the study population were under the recommended s-25(OH)D sufficiency level of ≥50 nmol/l.

Preventing vitamin D deficiency (VDD): a systematic review of economic evaluations.

Background: Vitamin D deficiency (VDD) is a public health concern worldwide. If untreated, it can lead to reduced quality of life and escalated costs brought about by ill-health. Preventive programmes to improve population vitamin D status exist but little is known about their cost-effectiveness. This information is vital so that decision-makers adopt efficient strategies and optimise use of public resources. Aims: Systematically review and critically appraise economic evaluations of population strategies to prevent VDD. Methods: The databases reviewed were MEDLINE, EMBASE, Econlit, NHS EED, CEA, and RepEc. All full economic evaluations of VDD prevention strategies were included. Interventions considered were food fortification, supplementation and public health campaigns. Data extracted included type of evaluation, population, setting, measure of benefit and main results. Results: Of the 2492 records screened, 14 studies were included. The majority of studies focused on supplementation within at-risk groups with the primary objective of either preventing fractures or falls in older adults. There was insufficient economic evidence to draw conclusions about the cost-effectiveness of population strategies. No study was identified that offered a direct comparison of the two main alternative population strategies: food fortification vs. supplementation. Conclusions: Whilst there is a growing body of evidence on the cost-effectiveness of micro nutrient programmes, there is a paucity of data on vitamin D fortification and how fortification programmes compare to population supplementation programmes. We highlight research gaps, and offer suggestions of what is required to undertake population-based cost-effectiveness analysis.

A randomized, controlled trial evaluating the efficacy of an online intervention targeting vitamin D intake, knowledge and status among young adults.

BACKGROUND: Vitamin D plays a key role in bone health. Consuming adequate vitamin D during young adulthood is important due to the development of peak bone mass; however, many Canadian young adults do not meet vitamin D recommendations. This study aimed to improve knowledge, perceptions, dietary intake and blood concentrations of vitamin D among a sample of young adults. METHODS: Using a pre-post design, 90 Ontario adults (38 men, 52 women; 18-25 years), were randomly assigned to intervention or control groups. Participants completed a socio-demographic survey, pre-post food frequency questionnaire, and a vitamin D knowledge questionnaire (3 time-points). The intervention group watched a video, received online information and tracked intake of vitamin D using a mobile application for 12 weeks. A sub-sample of participants completed pre-post blood 25(OH)D3 tests. Univariate ANOVA tested pre-post between-group differences in vitamin D intake and status. Repeated-measures ANOVA tested between-group differences in vitamin D knowledge and perceptions across 3 time-points. RESULTS: Mean vitamin D intake in the sample increased significantly from pre-test (M = 407, SD = 460 IU) to post-test (M = 619, SD = 655 IU), t(88) = 5.37, p < 0.001. Mean intake increased significantly more in the intervention than control group after controlling for gender and education, F(1, 85) = 4.09, p = 0.046. Mean blood vitamin D3 was significantly higher among non-Caucasian than Caucasian participants at baseline, t(56.7) = 3.49, p = 0.001. Mean blood vitamin D3 increased significantly from pre-test (M = 28, SD = 16 nmol/L) to post-test (M = 43, SD = 29 nmol/L), t(53) = 11.36, p < 0.001, but did not differ significantly between groups. The increase in vitamin D knowledge from time 1-3 was significantly higher in the intervention than control group (t(88) = 2.26, p = 0.03). The intervention group (M = 3.52, SE = 0.13) had higher overall perceived importance of vitamin D supplementation than the control (M = 3.16, SE = 0.12), F(1, 88) = 4.38, p = 0.04, ηp2 = 0.05. CONCLUSIONS: Although recommendations suggest blood 25(OH)D3 concentrations of ≥50-75 nmol/L, vitamin D status was below national recommendations. While participating in an intervention did not improve vitamin D status, it led to increased vitamin D intake, knowledge and perceived importance of supplementation. TRIAL REGISTRATION: ClinicalTrails.gov registration #: NCT02118129 .

Assessment of serum 25-hydroxyvitamin D concentrations of beef cows and calves across seasons and geographical locations.

Vitamin D is critical for the growth and development of calves and positively contributes to immune function of cattle. Serum 25-hydroxyvitamin D (25(OH)D) concentrations above 20 ng/mL have traditionally been considered adequate for growth and development of cattle, but recent evidence has indicated that concentrations below 30 ng/mL are insufficient for immunity. Because little information is available regarding vitamin D status of beef cattle, the objective of this study was to evaluate vitamin D status of beef cow-calf herds on pasture as affected by season and location. Serum samples were collected from 43 cow-calf pairs plus an additional 54 calves in herds located in Florida, Idaho, and Minnesota in the spring calving season. Samples were collected again over the summer months from animals in the Florida and Minnesota herds. Effects of subcutaneous injection of vitamins A, D, and E also were investigated in a subset of calves from the Idaho herd. All cows sampled had serum 25(OH)D concentrations above 30 ng/mL at the time of calving in the spring. The average serum 25(OH)D concentrations of cows rose from near 60 ng/mL in the spring to 75 ng/mL in the summer ( < 0.001). Most calves, on the other hand, had serum 25(OH)D concentrations below 20 ng/mL. The calves in the Florida and Minnesota herds similarly rose from averages of 10 to 15 ng/mL at birth to near 50 ng/mL by the end of summer. Serum 25(OH)D of severely deficient calves increased from 3 ng/mL in nonsupplemented calves to 11 ng/mL at 48 h after birth if given a bolus supplementation of 40,000 IU of vitamin D via subcutaneous injection of a vitamin A, D, and E supplement at birth ( < 0.001). Vitamin D supplementation of cows late in pregnancy has been shown to increase serum 25(OH)D of calves; however, beef cattle generally receive very little supplemental vitamin D, as was the case for the cows studied here. The lower serum 25(OH)D of cows in spring compared with summer and the prevalence of vitamin D deficiency of calves observed here indicate that increased vitamin D supplementation of cows over the winter months or vitamin D supplementation of newborn calves would be beneficial.

Seasonal Changes in Vitamin D-Effective UVB Availability in Europe and Associations with Population Serum 25-Hydroxyvitamin D.

Low vitamin D status is common in Europe. The major source of vitamin D in humans is ultraviolet B (UVB)-induced dermal synthesis of cholecalciferol, whereas food sources are believed to play a lesser role. Our objectives were to assess UVB availability (Jm(-2)) across several European locations ranging from 35° N to 69° N, and compare these UVB data with representative population serum 25-hydroxyvitamin D (25(OH)D) data from Ireland (51-54° N), Iceland (64° N) and Norway (69° N), as exemplars. Vitamin D-effective UVB availability was modelled for nine European countries/regions using a validated UV irradiance model. Standardized serum 25(OH)D data was accessed from the EC-funded ODIN project. The results showed that UVB availability decreased with increasing latitude (from 35° N to 69° N), while all locations exhibited significant seasonal variation in UVB. The UVB data suggested that the duration of vitamin D winters ranged from none (at 35° N) to eight months (at 69° N). The large seasonal fluctuations in serum 25(OH)D in Irish adults was much dampened in Norwegian and Icelandic adults, despite considerably lower UVB availability at these northern latitudes but with much higher vitamin D intakes. In conclusion, increasing the vitamin D intake can ameliorate the impact of low UVB availability on serum 25(OH)D status in Europe.

Predictors of Vitamin D-Containing Supplement Use in the Australian Population and Associations between Dose and Serum 25-Hydroxyvitamin D Concentrations.

Despite concerns about vitamin D deficiency in the Australian population, little is known about the prevalence and predictors of vitamin D-containing supplement use. We described the use of vitamin D-containing supplements, and investigated associations between supplemental vitamin D intake and serum 25-hydroxyvitamin D (25(OH)D) concentrations, using a single 24-h dietary recall from the 2011-2013 Australian Health Survey (n = 12,153; ages ≥ 2 years). Multiple regression models were used to investigate predictors of vitamin D-containing supplement use in adults, and associations between dose and serum 25(OH)D concentrations/vitamin D sufficiency (≥50 nmol/L), adjusting for potential confounders. The prevalence of vitamin D-containing supplement use was 10%, 6% and 19% in children, adolescents and adults, respectively. Predictors of vitamin D-containing supplement use in adults included being female, advancing age, higher educational attainment, higher socio-economic status, not smoking, and greater physical activity. After adjusting for potential confounders, a 40 IU (1 µg) increase in vitamin D intake from supplements was associated with an increase of 0.41 nmol/L in serum 25(OH)D concentrations (95% CI 0.35, 0.47; p < 0.001). However, the prevalence of vitamin D-containing supplement use was generally low in the Australian population, particularly for single vitamin D supplements, with most supplement users obtaining only low levels of vitamin D from other supplement types.

[Implementation of the Dutch vitamin D supplementation advice: report of an expert meeting]. / Implementatie van het vitamine D-advies. Verslag van een expertmeeting.

In 2012, the Dutch Health Council published updated advice on vitamin D supplementation in the population of the Netherlands. Although implementation of the advice has commenced, progress is slow. The bottlenecks in implementation were highlighted at a national expert meeting and ideas formulated for improvements. Implementation is rendered more difficult because of the complex mix of lack of awareness of the advice, the reimbursement system of the health insurance companies and a lack of clarity regarding price and dosage differences of the supplements. Existing contact opportunities with healthcare professionals, such as when the flu vaccination is given, need to be used to provide information so as to improve the implementation. The children's health clinic can be used to inform the whole family about supplementation. In nursing and care homes, vitamin D supplementation should be instituted as standard and seen as an indicator of responsible care. It is important to prioritize target groups. The initial focus must be on the most vulnerable group, the inhabitants of nursing and care homes. The second priority must be given to the elderly living independently and to non-western immigrants.

Vitamin D deficiency in minority populations.

OBJECTIVE: Black and Hispanic individuals synthesize less vitamin D per unit of sun exposure than white individuals. The relationship between UV radiation and vitamin D insufficiency in minorities has not been well explored. DESIGN: Prospective cohort study. SETTING: Using the National Health and Nutrition Examination Survey, we obtained serum vitamin D levels for non-Hispanic Whites, Hispanics and non-Hispanic Blacks aged ≥18 years from 2000-2006. We linked these data with the average monthly solar UV index by census tract and data on sun exposure, vitamin D supplementation, health and demographics. We used multivariable regression analyses to assess vitamin D deficiency (<15 ng/ml) and insufficiency (<20 ng/ml) in January (when the UV index was lowest) by race/ethnicity and geography. SUBJECTS: Adults (n 14,319) aged ≥18 years. RESULTS: A 1-point increase in the UV index was associated with a 0·51 ng/ml increase in vitamin D (95% CI 0·35, 0·67 ng/ml; P<0·001). Non-Hispanic Black race and Hispanic ethnicity were associated with a 7·47 and 3·41 ng/ml decrease in vitamin D, respectively (both P<0·001). In January, an estimated 65·4% of non-Hispanic Blacks were deficient in vitamin D, compared with 28·9% of Hispanics and 14·0% of non-Hispanic Whites. An estimated 84·2% of non-Hispanic Blacks were insufficient in vitamin D v. 56·3% of Hispanics and 34·8% of non-Hispanic Whites. More non-Hispanic Blacks were estimated to be deficient in vitamin D in January in the highest UV index quartile than were non-Hispanic Whites in the lowest UV index quartile (60·2% v. 25·7%). CONCLUSIONS: Wintertime vitamin D insufficiency is pervasive among minority populations, and not uncommon among non-Hispanic Whites.

Assessment of vitamin D status in children aged 1-5 with simple obesity.

BACKGROUND: Proper vitamin D intake is important due to its pleiotropic effect. It seems that obese population is a groups at risk of the vitamin D deficiency. OBJECTIVE: To assess the vitamin D status in 1-5-year-old children with simple obesity. MATERIALS AND METHODS: The study included 100 children: classified according to their body mass index (BMI) as obese - Group I (n=50) and non-obese - Group II (n=50). Their serum 25-hydroxyvitamin D (25(OH)D) concentrations were determined in the spring-summer and autumn-winter seasons and vitamin D intake (diet/supplements) was assessed. The study results were statistically analysed by means of Statistica 10PL. RESULTS: In Group I the mean serum 25(OH)D level was 23.6±10.8 ng/ml, while in Group II it reached 26.6±9.8 ng/ml (p=0.08). The concentration ≤30 ng/ml was observed in 80% of children in Group I and in 70% of Group II. In autumn- winter and spring-summer period, respectively, 88.5% and 70.9% of the obese children had an insufficient vitamin D status (p=0.002). The mean daily intake of vitamin D was 128 IU (3.2 µg) in Group I and 188 IU (4.7 µg) in Group II. CONCLUSIONS: Children aged 1-5 (obese and non-obese) are a group at risk of the vitamin D deficiency, as a consequence of its insufficient intake and the lack of appropriate supplementation. Those particularly exposed to that risk are obese children in the autumn-winter season. Children aged 1-5 should be monitored with regard to their vitamin D status. KEY WORDS: vitamin D, obesity, children, obese children, vitamin D deficiency.

Vitamin D supplementation in pregnancy: a systematic review.

BACKGROUND: It is unclear whether or not the current evidence base allows definite conclusions to be made regarding the optimal maternal circulating concentration of 25-hydroxyvitamin D [25(OH)D] during pregnancy, and how this might best be achieved. OBJECTIVES: To answer the following questions: (1) What are the clinical criteria for vitamin D deficiency in pregnant women? (2) What adverse maternal and neonatal health outcomes are associated with low maternal circulating 25(OH)D? (3) Does maternal supplementation with vitamin D in pregnancy lead to an improvement in these outcomes (including assessment of compliance and effectiveness)? (4) What is the optimal type (D2 or D3), dose, regimen and route for vitamin D supplementation in pregnancy? (5) Is supplementation with vitamin D in pregnancy likely to be cost-effective? METHODS: We performed a systematic review and where possible combined study results using meta-analysis to estimate the combined effect size. Major electronic databases [including Database of Abstracts of Reviews of Effects (DARE), Centre for Reviews and Dissemination (CRD), Cochrane Database of Systematic Reviews (CDSR) and the Health Technology Assessment (HTA) database] were searched from inception up to June 2012 covering both published and grey literature. Bibliographies of selected papers were hand-searched for additional references. Relevant authors were contacted for any unpublished findings and additional data if necessary. Abstracts were reviewed by two reviewers. SUBJECTS: pregnant women or pregnant women and their offspring. EXPOSURE: either assessment of vitamin D status [dietary intake, sunlight exposure, circulating 25(OH)D concentration] or supplementation of participants with vitamin D or food containing vitamin D (e.g. oily fish). OUTCOMES: offspring - birthweight, birth length, head circumference, bone mass, anthropometry and body composition, risk of asthma and atopy, small for gestational dates, preterm birth, type 1 diabetes mellitus, low birthweight, serum calcium concentration, blood pressure and rickets; mother - pre-eclampsia, gestational diabetes mellitus, risk of caesarean section and bacterial vaginosis. RESULTS: Seventy-six studies were included. There was considerable heterogeneity between the studies and for most outcomes there was conflicting evidence. The evidence base was insufficient to reliably answer question 1 in relation to biochemical or disease outcomes. For questions 2 and 3, modest positive relationships were identified between maternal 25(OH)D and (1) offspring birthweight in meta-analysis of three observational studies using log-transformed 25(OH)D concentrations after adjustment for potential confounding factors [pooled regression coefficient 5.63 g/10% change maternal 25(OH)D, 95% confidence interval (CI) 1.11 to 10.16 g], but not in those four studies using natural units, or across intervention studies; (2) offspring cord blood or postnatal calcium concentrations in a meta-analysis of six intervention studies (all found to be at high risk of bias; mean difference 0.05 mmol/l, 95% CI 0.02 to 0.05 mmol/l); and (3) offspring bone mass in observational studies judged to be of good quality, but which did not permit meta-analysis. The evidence base was insufficient to reliably answer questions 4 and 5. LIMITATIONS: Study methodology varied widely in terms of study design, population used, vitamin D status assessment, exposure measured and outcome definition. CONCLUSIONS: The evidence base is currently insufficient to support definite clinical recommendations regarding vitamin D supplementation in pregnancy. Although there is modest evidence to support a relationship between maternal 25(OH)D status and offspring birthweight, bone mass and serum calcium concentrations, these findings were limited by their observational nature (birthweight, bone mass) or risk of bias and low quality (calcium concentrations). High-quality randomised trials are now required. STUDY REGISTRATION: This study is registered as PROSPERO CRD42011001426. FUNDING: The National Institute for Health Research Health Technology Assessment programme.